A waveguide filter is a passive filter used in microwave technology in the form of a specifically equipped waveguide. It serves to suppress or to let pass specific frequencies of the electromagnetic wave propagating in the waveguide. Among other things, waveguide filters may be used as an assembly for larger transmitter systems, radar systems, and for communication satellites.
Huge fluctuations in temperature may occur particularly in aerospace applications, which fluctuations in temperature may become effective as intense changes of the volume of waveguide components and waveguide filters. One solution for avoiding temperature dependencies (drift) of waveguide filters is the selection of materials which have a very low temperature expansion coefficient by nature, e.g., invar. However, materials like invar have the drawback that they are heavy-weight, expensive, and difficult to process.
Another solution for avoiding temperature dependencies of waveguide filters is using additional mechanical elements, like bimetal structures which physically compensate the temperature dependent expansion of the waveguide by a temperature dependent deflection of the bimetal structure which deflection is opposite in its effect. For example, German patent document DE 43 19 886 C1 discloses an arrangement for compensating temperature dependent changes of the volume of a waveguide, wherein the waveguide is clamped in a frame, wherein the temperature dependent expansion of the frame is lower than that one of the waveguide. The waveguide is connected to the frame in a force-fitting manner (friction lock) at at least two positions of its wall being arranged opposite to each other and the friction lock connections between the frame and the waveguide are accomplished by distance pieces (spacers) which transfer pressure and tensile forces to the waveguide wall and cause deformation there, wherein the pressure and tensile forces result from a different heat expansion of the frame and the waveguide. Such a mechanic solution is depicted in the following, but has the drawback, among other things, that it is costly in manufacturing and handling.